Chronic carbohydrate restriction improves endurance capacity and body composition in men and women

Abstract

This study was designed to test whether adaptation to a CHO-restricted diet affects physical capacity during prolonged exercise. It is hypothesised that chronically reducing an individual’s dietary carbohydrate intake during training will increase their maximal rate of fatty acid oxidation during subsequent exercise compared to a chronic high carbohydrate diet. Thirteen highly trained endurance athletes (eight males, VO2max 66.0 ± 9.5 ml/kg/min, five females VO2max 50.6 ± 8.4 ml/kg/min) consumed a high (>5 g CHO/kg/day) or low (<2 g CHO/kg/day) carbohydrate training diet for four weeks in a randomized cross-over design. Performance was measured after a 24 h high carbohydrate “loading” regime, through a self-paced time trial to complete a fixed workload equivalent to five hours at a workload calculated to elicit 55% VO2max. Although time to completion was not significantly different between diets, the average absolute (watts) and relative (W/kg) power outputs were significantly better on the carbohydrate restricted diet (p = 0.03 and 0.02 respectively). Both sexes responded similarly in terms of performance whilst only women significantly improved body composition when carbohydrate was restricted (p = 0.02). Results from this study highlight that when carbohydrate is restricted during training, trained endurance athletes show improved ultra-endurance performance relative to their body mass.